The objective of this study was to evaluate by immunohistochemical means nuclear reactivity for Mdm2 and p53 proteins in 71 canine cutaneous mast cell tumours. Detectable reactivity for Mdm2 was observed in 17 of 23 grade I tumours, 19 of 27 grade II tumours, and 14 of 21 grade III tumours, the grading method used was that by Patnaik et al. [Vet. Pathol., vol. 21, 1984, p. 469]. Increased reactivity for Mdm2 was detected in grade III tumours compared with grade I tumours. In contrast to Mdm2, detectable reactivity for p53 was observed in 17 tumours. Of 39 cases with moderate or marked Mdm2, 34 showed mild or no detectable p53, although only five showed moderate or marked p53. The results suggest that Mdm2 overexpression plays a crucial role in canine mast cell tumorigenesis and is consistent with the histologic grade, and its expression may be induced without p53 overexpression.

Abstract. The objective of this study was to evaluate by immunohistochemical means the nuclear expression of p27 and p21 proteins in cutaneous mast cell tumors and histiocytomas of dogs. In mast cell tumors, nine of the 13 grade I tumors, 13 of the 19 grade II tumors, and 10 of the 15 grade III tumors showed no detectable or mild p27 immunoreactivity. In contrast, one of the 13 grade I tumors, 12 of the 19 grade II tumors, and 11 of the 15 grade III tumors showed moderate or marked p21 immunoreactivity. Nineteen of the 28 histiocytomas showed no detectable or mild p27 immunoreactivity, and 24 cases showed moderate or marked p21 immunoreactivity. These findings indicate that a loss or absence of p27 expression is an early pathogenic event in mast cell and histiocyte tumorigenesis and that p21 expression may be a marker of mast cell tumor progression and histiocytoma cell proliferation.

The TP53 tumor suppressor protein (formerly known as p53) responds to a wide variety of environmental insults. To evaluate the safety of cellular telephones, TP53 responses in human fibroblast cells were studied after exposure to 837 MHz microwaves. Cells were exposed in a temperature-controlled transverse electromagnetic (TEM) chamber to a specific absorption rate (SAR) of 0.9 or 9.0 W/kg at 837 MHz continuous-wave (CW) microwave irradiation for 2 h. The TP53 protein levels were measured by Western blot at 2, 8, 24 and 48 h after treatment. The TP53 protein levels in microwave-treated cells, sham-treated cells, and untreated cells remained unchanged relative to each other at all times tested (Fisher test and Student-Newman-Keuls test, P > 0.05). No morphological alterations were observed in microwave-treated cells compared to sham-treated cells. We conclude that TP53 protein expression levels in cultured human fibroblast cells do not change significantly during a 48-h period after exposure to 837 MHz continuous microwaves for 2 h at SAR levels of 0.9 or 9.0 W/kg.

ABSTRACT. 3-methylcholanthrene (MC)-induced mouse 10 embryonal (ERSs) and 24 pleomorphic rhabdomyosarcomas (PRSs) of the dermis were examined immunohistochemically for nuclear reactivity of Mdm2, p53, and proliferating cell nuclear antigen (PCNA). ERSs were microscopically present in the rhabdium layer of the dermis from 10 to 13 weeks post injection (PI), and PRSs developed from 13 weeks PI. Moderate to marked Mdm2 reactivity was observed in each of the 10 ERSs, and 23 of the 24 PRSs. Moderate to marked p53 reactivity was observed in 5 of the 10 ERSs, and 19 of the 24 PRSs. p53 reactivity increased in PRSs compared with ERSs. The level of Mdm2 expression was significantly higher compared with p53 expression. Discordant Mdm2 overexpression was observed in 5 ERSs and 5 PRSs, and discordant p53 overexpression was observed in 1 PRSs, although co-overexpression of Mdm2 and p53 was observed in 5 ERSs and 18 PRSs. PCNA reactivity significantly increased in PRSs compared with ERSs. These results suggest that Mdm2 overexpression is an important pathogenic event in MC-induced mouse rhabdomyosarcomas, and its expression may be induced by p53-independent pathway. KEY WORDS: MC, Mdm2, mouse, p53, rhabdomyosarcoma.J. Vet. Med. Sci. 68 (5): [427][428][429][430][431] 2006 The Mdm2 oncogene was first identified as an amplified gene on a murine double-minute chromosome in the 3T3DM cell line, a spontaneously transformed derivative of BALB/c 3T3 cells [3]. Mdm2 has been shown to interact with a group of cell cycle-related proteins, including the retinoblastoma protein [29], E2F1 and DP1 transcription factors [14], and transforming growth factor-beta [23]. Mdm2 overexpression is frequent in soft tissue and bone tumors in human beings [2,8,13,30] and dogs [16,22].The tumor suppressor gene p53 plays a key role in the control of the cell cycle, maintenance of genomic stability, and programmed cell death [12,27]. p53 mutations are common in methylcholanthrene-induced mouse tumors [4], and have been identified in several types of human neoplasms [18,21]. The Mdm2 protein directly binds to p53 protein and inhibits the transcriptional function of p53 protein and also targets it for degradation via the ubiquitin-proteasome pathway [15,27].Rhabdomyosarcoma is the most common malignant soft tissue sarcoma in childhood and adolescence. Recently, it has been reported that Mdm2 is expressed at low levels and does not show differences between subtypes of rhabdomyosarcomas of human beings [11,24,25]. However, little is known about the mechanism of tumorigenesis of rhabdomyosarcoma. Expression of Mdm2 and p53 has not been investigated in methylcholanthrene-induced rhabdomyosarcomas, although expression of some differentiation markers such as vimentin, desmin, and myoglobin has been studied [9,26]. Thirty-four rhabdomyosarcomas were induced by subcutaneous injection of 3-methylcholanthrene (MC) in C3H/HeJ mice. In this study, we examined nuclear reactivity of Mdm2 and p53 proteins by immunohistochemistry in MC-induced mouse rhabdomyosarcomas, a...

ABSTRACT. The objective of this study was to evaluate nuclear reactivity of Mdm2 and p53 proteins by immunohistochemical means in feline mammary gland tumors; 12 adenomas which included 6 adenomatous lesions obtained from the tissue adjacent to adenocarcinomas, and 22 adenocarcinomas. Seven adenomas and 18 adenocarcinomas showed moderate or marked Mdm2 reactivity. Sixteen adenocarcinomas showed moderate to marked p53 reactivity, but 9 adenomas showed none. Discordant Mdm2 overexpression was found in 5 adenomas and 3 adenocarcinomas, although co-overexpression of Mdm2 and p53 was found in 15 adenocarcinomas. These results suggest that nuclear overexpression of Mdm2 is present in the tumors of early stage without p53 overexpression and related to feline mammary gland tumorigenesis. Nuclear overexpression of p53 is more frequent in adenocarcinomas, but not in adenomas. KEY WORDS: feline mammary tumor, Mdm2, p53.J. Vet. Med. Sci. 68(5): 421-425, 2006 Mammary neoplasm is the third most common tumor, following lymphoid and cutaneous neoplasms in cats and simple type adenocarcinoma, and complex type tumor and myoepithelioma are found rarely [12]. The molecular and genetic events contributing to feline mammary gland tumorigenesis are largely unknown.Mdm2 (murine double minute-2) gene was first cloned as an amplified gene in a spontaneously transformed mouse 3T3 DM cell line [9]. Mdm2 has been shown to interact with a group of cell cycle-related proteins, including the retinoblastoma protein [19], the transcription factor E2F1 [32], and transforming growth factor-beta [28]. Mdm2 is frequently overexpressed in soft tissue sarcomas in human beings [6] and dogs [25,27], and also in some human epithelial neoplasms, such as those of the breast [10,18] The function of p53 tumor suppressor is a principal mediator of growth arrest, senescence, and apoptosis in response to a broad array of cellular damage [17,31]. Mdm2 protein binds to p53 protein, and both proteins regulate each other; one effect is to inhibit the transcriptional transactivation activity of p53, resulting in negative regulation of the tumor suppression function of p53 [21,30]. p53 protein regulates Mdm2 gene at the level of transcription by an intronic promotor. This creates a feedback loop that regulates both the activity of p53 protein and the expression of Mdm2 gene [21,30]. Overexpression of p53 protein has been reported in feline mammary gland tumors and squamous cell carcinomas [22], and in human malignant epithelial tumors of the breast [3], stomach [13], kidney [11], and liver [7].The expression of Mdm2 in feline mammary gland tumors has not been studied. The purpose of this study was to better understand the mechanisms of feline mammary gland tumorigenesis by immunohistochemical means for the nuclear reactivity of Mdm2 and p53 proteins and the relationship between expression of these molecules. MATERIALS AND METHODS Tumors:The samples were collected from feline mammary tumors removed surgically during a 5-year period at Yamaguchi University. The samp...